This invention relates to delivery devices, particularly pharmaceutical tablets, and methods for making thereof.
Pharmaceutical tablets are often administered orally. A rapid disintegration of the tablet in the mouth without mastication or water facilitates administration to patients in general, and to the very young, the elderly, and to non-human animals, in particular.
One type of oral dosage form which is designed to address the problem of swallowing is known as "chewable tablets". These tablets, however, are not fully satisfactory because they require mastication.
Another type of oral dosage form known as the "effervescent tablet" comprises solid adjuvants of an acid and a base. The reaction between the acid and the base in the presence of water gives off carbon dioxide which "blows apart" the tablet to facilitate its dissolution. One type of effervescent tablet that must dissolve in a glass of water for administration requires that the patient drink the water. Aside from the problem of leaving a small amount of residual active agent in the glass, this dosing method is impractical for very young patients. Another type of effervescent tablet that "bubbles" and then dissolves in the mouth is also objectionable to some patient populations, especially the very young. Both types of effervescent tablets are thus not fully satisfactory.
Yet another type of oral dosage form known as the "enteric tablet" is designed to release the pharmaceutical agent in the upper small intestine. A limitation of enteric tablets is that those that fail to disintegrate rapidly in the intestine could pass the "window of absorption" and result in poor bioavailability.
One type of non-oral dosage form known as the birth control pessaries often takes as long as ten minutes to release the foaming agent. For obvious reasons, it is desirable for this type of dosage form to disintegrate rapidly.
Tablets that disintegrate rapidly in an aqueous environment are often formulated with disintegration agents, such as starch, microcrystalline cellulose, carboxymethylcellulose sodium, and sodium starch glycolate, etc. These tablets disintegrate at an unsatisfactory rate for some applications described above.
An increased disintegration rate can be obtained by increasing the porosity (void spaces) of the tablet. Void spaces in the tablet matrix facilitate the permeation of water to rapidly erode the entire tablet. It is easily understood that a higher porosity of the tablet implies a faster disintegration in an aqueous environment. It is therefore desirable to obtain tablets of the highest porosity technically achievable.
U.S. Pat. No. 3,885,026 discloses a process for the production of porous tablets. In this process, a solid volatilizable adjuvant is incorporated in the tablet formulation. The tablet is formed by compression, and the volatilizable adjuvant is removed by sublimation or thermal decomposition. Exemplary volatilizable adjuvant include urethane, urea, ammonium bicarbonate, hexamethylenetetramine, benzoic acid, phthalic anhydride, naphthalene and camphor. The maximum porosity obtained according to this patent is 50% and preferably 10 to 30%. Strong tablets of a porosity higher than 50% are difficult to produce by this method.
U.S. Pat. No. 4,134,943 discloses the production of porous tablets by mixing the tablet components with a liquid solvent which is inert towards the tablet components. Suitable solvents include water, cyclohexane, benzene, etc., which freeze at a temperature from about -30.degree. to +25.degree. C. The solvent constitutes about 5 to 80% by weight of the total mixture. The mixture is divided or sprayed into small particles or droplets which are subsequently frozen into solid flowable granules. These granules are pressed into tablets at a temperature below the freezing point of the solvent, and then the solvent is sublimed from the tablets. The porosity of the resultant tablets corresponds to the amount of solvent that is removed from the tablet. The maximum porosity of the tablets produced by this method is 80%. The method of production in this patent is relatively complex since it involves the preparation of frozen granules.
Finally, U.S. Pat. Nos. 4,305,502 and 4,371,516 disclose the production of shaped articles by freezing, in a mold, a water-based pharmaceutical composition, and subliming the water from the frozen composition to form porous articles. These processes do not include compression of the articles and therefore lack the ability to produce a specifically desired shape of the article on the side of the mold that is open. Because the articles produced by this process have weak, easily broken meniscuses, U.S. Pat. No. 4,305,502 reduces the amount of handling of the articles by forming them in situ in the depressions of a filmic packaging substrate. The method in both patents allows only one side of the article to be imprinted. It is therefore difficult to include both the company logo and the drug identification on one dose unit as usually desired.
Although there are a variety of methods for making porous tablets, these methods do not adequately address all the problems. For example, processes are complex, tablets lack sufficient porosity, tablets are not shaped, tablets are weak and fragile. Accordingly, there is a continual search in this art for highly porous, strong, shaped tablets.